Interaction between emissions of SO₂ and HCl in fluidized bed combustors

The ability to capture SO₂ and halogens is one of the most important advantages of fluidized bed combustion (FBC). In order to clarify the affects of chlorine in the absorption of SO₂ emission, experiments involving the addition of PVC to coils were carried out using the 0.3 m ID bench scale FBC system at Western Kentucky University. During the experiments, PVC was added to three coals in different percentages, and the mixtures fed into the FBC system. The Ca/S ratio was kept constant at 3:1. The experimental results indicate that chloride addition dramatically decreased the SO₂ concentration in flue gases. The sulfur and chlorine contents in both fly ash and bed ash increased. At the same time, the utilization efficiency of calcium increased with an increase in the PVC weight percent. This reduction in SO₂ is attributed to more voids on the sorbent particle surface (limestone and/or ash) through transient formation of a mobile halide ion-containing phase (CaCl₂), and to the reactions. 4HCl+O₂↔2Cl₂+2H₂O Cl₂+SO₂+H₂O↔2HCl+SO₃. A proposed mechanism involving the interaction between SO₂ and HCl is discussed in detail.